1. Field of the Invention
The present invention is directed to the field of angioplasty and, in particular, to a multi-lumen dilation catheter having variable stiffness along the length of the catheter to provide sufficient pushability while maintaining distal flexibility.
2. Description of the Prior Art
Angioplasty has gained wide acceptance in recent years as an efficient and effective method for treating certain types of vascular diseases. In particular, angioplasty is widely used for expanding a constricted area or lesion in a coronary artery. It is also used for treatment of lesions in other parts of the vascular system as well.
The most widely used form of angioplasty makes use of a balloon dilation catheter which is introduced into a patient's vascular system and is positioned across a stenosis. The balloon is inflated by supplying fluid under pressure through an inflation lumen connected to the balloon. The inflation of the balloon imparts a stretching force to the stenosis or artery wall to reestablish an acceptable blood flow through the artery.
There are various types of catheters available and one category of catheter is referred to as an over the wire (OTW) catheter. An OTW catheter is used in conjunction with a separate guide wire to cross a narrowed site in a person's vascular system. In this type of procedure, the guide wire is first advanced through the vasculature to or near the site of the lesion. After the guide wire is properly positioned, the catheter is advanced or guided over the guide wire so that the balloon portion is at the narrowed site.
OTW angioplasty balloon catheters generally have one of two types of construction, a coaxial construction or a multi-lumen construction. The coaxial construction has an inner tube which defines an inner lumen and an outer tube coaxially disposed about the inner tube to define an outer lumen between the walls of the tubes. The inner lumen typically will have a guide wire running therethrough while the outer lumen conveys inflation fluid from the proximal end of the catheter to the inflatable balloon. The multi-lumen design has a catheter shaft formed from a singular tubular extrusion with two or more lumens extending longitudinally and side-by-side through the shaft. One lumen is occupied by a guide wire and the other lumen(s) is (are) used to convey an inflation fluid from the proximal end of the catheter to the inflatable balloon.
Each design provides certain advantages. One advantage of the coaxial design, for example, is that the proximal portion of the outer tube can be formed from a relatively stiff material to provide increased "pushability" to the catheter. Another advantage is that the outer and inner tubes can be necked down in the distal region of the catheter and under the proximal waist of the balloon to reduce the distal shaft diameter and the profile of the catheter in its deflated state. A further advantage is that the coaxial design is symmetrically flexible in all directions. In addition, the coaxial catheter allows some degree of relative movement to take place between the inner tube and the outer tube when the catheter is bent which also increases the flexibility.
One advantage of the dual lumen design is its simple construction. First, only a single tube is extruded even though the number of lumens therein may vary. Secondly, there are fewer pieces associated with a dual lumen catheter thereby reducing the cost of fabrication and the complexity of assembly.
Dual lumen designs, however, have some disadvantages typically not associated with coaxial catheters. As discussed above, generally, dual lumen catheters have uniform flexibility over the entire shaft length and are often less flexible than coaxial catheters over the distal shaft because they are formed from a single extrusion tube. There have been efforts, however, to increase the flexibility of dual lumen catheters.
For example, Maguire et al., U.S. Pat. No. 4,782,834, discloses a dual lumen dilation catheter having a plurality of sections of different stiffness to provide optimum strength and flexibility at different points along the length of the catheter. The plurality of sections of the catheter are joined together by heat melting to form a unitary structure.
Conway et al., U.S. Pat. No. 4,877,031, discloses a dilation catheter which perfuses blood distally of the dilation balloon during inflation thereof. The lumen used for the distal perfusion of blood is separate from the lumen receiving the guide wire. The catheter may have a tubular structure formed from a material such as polyimide with an outer coating of resin impregnated fibrous material which has been wound or braided into the tubular substructure to provide a relatively stiff proximal portion and a relatively flexible but diametrically rigid distal portion.